The process for starting a gas turbine engine is a complicated procedure which requires continual monitoring of various engine parameters to avoid damaging engine components. One potentially damaging condition which may arise during engine startup is a hot start. The exact cause of a hot start condition in a gas turbine engine has been the subject of much speculation and theory, however, the detection of the occurrence of a hot start condition is well known.
A hot start condition occurs when the temperature of the working fluid exiting the turbine section of the gas turbine engine exceeds, by a certain amount, the expected exhaust gas temperature schedule for the engine during a normal startup. As will be appreciated by those skilled in the art, an unaddressed hot start condition can cause the gas temperature in the turbine section to exceed allowable material temperature limits, thereby shortening or ending the life of internal engine components such as blades, disks, seals, etc. Typical engine starting procedures therefore call for careful monitoring of the exhaust gas temperature, and immediate shutdown of the startup sequence should exhaust gas temperature exceed the appropriate limit.
As will further be appreciated, the shutdown of a startup sequence is particularly inconvenient as it requires the engine rotor to remain turning under the influence of the engine starter motor for a sufficient period of time to clear all fuel and combustion products from the engine. The entire startup sequence is then reinitiated. The resulting delay can become particularly costly, particularly in today's congested air traffic environment when a few minutes' departure delay can disrupt busy airport scheduling.